Ssq1 is a specialized mitochondrial matrix Hsp70 ATPase in budding yeast. It couples its nucleotide cycle to engagement of the Isu1/Isu2 iron-sulfur cluster scaffold and promotes transfer of newly assembled clusters to the carrier Grx5. The J-protein Jac1 recruits the scaffold and stimulates Ssq1 ATP hydrolysis, while Mge1 promotes nucleotide exchange. This machinery supports maturation of mitochondrial and extramitochondrial Fe-S proteins. Ssq1 arose through duplication of the mitochondrial Hsp70 gene and differs from the abundant, multifunctional Ssc1 in client and cochaperone specificity. Loss of SSQ1 causes conditional growth defects, impaired Fe-S protein maturation and mitochondrial iron accumulation; Ssc1 can partially compensate when its expression is increased. Ssq1 also binds unfolded proteins and suppresses aggregation in vitro. Its contribution to Yfh1 precursor maturation is experimentally observed, although the molecular mechanism and its contribution to the broader mutant phenotypes remain unresolved.
Definition: Binding and ATP-dependent remodeling of an iron-sulfur cluster scaffold protein to promote transfer of a nascent iron-sulfur cluster from the scaffold to an acceptor protein.
Justification: Ssq1 binds client/scaffold proteins in an ATP-regulated Hsp70 cycle, is stimulated by Jac1 and Isu1, and promotes transfer of nascent Fe-S clusters from Isu1 to Grx5. The live ATP hydrolysis term is too generic for this direct chaperone role, while GO:0140662 would overstate Ssq1 as an ATP-dependent protein foldase and GO:0140309 would misdescribe the carried substrate as an unfolded protein delivered to a defined acceptor.
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Cytoplasm includes the mitochondrial compartment in which Ssq1 acts. Reason: The current Q05931 lineage descends from the cytoplasm IBD at PTN002321897, and matrix localization is independently supported by target studies. A broad, correct compartment is part of the core localization; it does not imply a separate soluble cytosolic pool. The more precise matrix annotation does not invalidate this ancestor. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002321897 SUPPORTS TRANSFER The current IBD and root-to-Q05931 tree path were verified; target SGD:S000004361 is among experimentally grounded descendants. Mitochondrial matrix is within cytoplasm. SGD:S000004361 SUPPORTS TRANSFER The current PTN002321897 donor set includes the target's own experimental cytoplasm grounding, which is valid IBD support rather than circularity. UniProtKB:P38646 SUPPORTS TRANSFER Human mitochondrial HSPA9/mortalin is a current descendant donor supporting cytoplasm for the same broad Hsp70 family compartment. PomBase:SPAC664.11 SUPPORTS TRANSFER The current donor set includes a fission-yeast mitochondrial Hsp70, supporting cross-fungal retention of the broad cytoplasm assertion. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: Mitochondria are the core compartment of Ssq1-mediated Fe-S maturation. Reason: Ssq1 performs its established Fe-S transfer role in the mitochondrial matrix. The organelle parent represents that core location and is not downgraded because a matrix child term also exists. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000452554 SUPPORTS TRANSFER The current mitochondrial IBD is on the exact target lineage and includes target experimental grounding. SGD:S000004361 SUPPORTS TRANSFER Ssq1 itself is one of the current experimentally grounded descendants used to place the mitochondrial node. UniProtKB:P38646 SUPPORTS TRANSFER Human HSPA9/mortalin supports the conserved mitochondrial-matrix Hsp70 branch containing Ssc1/Ssq1-like proteins. PomBase:SPAC664.11 SUPPORTS TRANSFER Fission-yeast evidence in the current donor set supports the eukaryotic mitochondrial Hsp70 compartment assertion. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0016887 ATP hydrolysis activity | IBA GO_REF:0000033 | ACCEPT | Summary: ATP hydrolysis powers the specialized Ssq1 chaperone cycle. Reason: Full PMID:12756240 measures single-turnover ATP-to-ADP conversion and steady-state activity of purified Ssq1. Jac1 and Isu1 act cooperatively; Mge1 supports nucleotide release and cycling. These direct catalytic measurements support the current family-level ATPase transfer. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000452648 SUPPORTS TRANSFER The current conserved Hsp70 ATPase IBD is on the target path. Target SGD:S000004361 is valid experimental grounding, not circular support. SGD:S000004361 SUPPORTS TRANSFER Target ATPase biochemistry is present among the current PAINT descendants and supports inheritance of Hsp70 ATP hydrolysis activity. PomBase:SPAC664.11 SUPPORTS TRANSFER A fungal mitochondrial Hsp70 descendant contributes to the current ancestral ATPase placement. UniProtKB:P38646 SUPPORTS TRANSFER Human HSPA9/mortalin supports ATP hydrolysis across the mitochondrial Hsp70 branch, consistent with direct Ssq1 measurements. Supporting Evidence: PMID:12756240 Jac1 and Isu1 cooperatively stimulate the ATPase activity of Ssq1. |
| GO:0031072 heat shock protein binding | IBA GO_REF:0000033 | ACCEPT | Summary: Chaperone-system partner binding supports Ssq1 function. Reason: The ancestral heat-shock-protein interaction capacity is compatible with the functional chaperone system of Ssq1. Direct target biochemistry establishes nucleotide-sensitive interaction with the GrpE-family cochaperone Mge1 (PMID:11601843, PMID:12756240). This interaction resets the core ATPase cycle; specificity for Jac1 rather than Mdj1 does not imply loss of all ancestral chaperone interactions. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000452648 SUPPORTS TRANSFER Actual ancestral interaction IBD verified. Core Mge1-dependent nucleotide cycling supports retention; no inference that every Hsp70 partner is interchangeable. UniProtKB:P0DMV8 SUPPORTS TRANSFER A human Hsp70 descendant in the current heat-shock-protein-binding donor set supports ancestral cochaperone binding at PTN000452648. UniProtKB:P11142 SUPPORTS TRANSFER A human HSC70 descendant also seeds the same current PAINT interaction node; Ssq1-specific Mge1 biochemistry supports transfer to Q05931 despite partner specialization. Supporting Evidence: PMID:11601843 Ssq1 was able to form a specific complex with the nucleotide exchange factor Mge1. |
| GO:0044183 protein folding chaperone | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: The broad protein-folding-chaperone IBA is a plausible non-core Hsp70-family inference. Reason: The current folding-chaperone IBD at PTN000452648 lies on the Ssq1 lineage, with no recorded NOT/IRD loss along that path. The focused report supports Ssq1 holdase and unfolded-substrate-binding capacity while finding no target assay that demonstrates productive refolding or ATP-driven restoration of a denatured substrate. Keep the broad ancestral protein-folding-chaperone inference as non-core, but do not refine it to ATP-dependent protein folding chaperone or treat it as Ssq1's defining ISC-transfer activity. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN000452648 SUPPORTS TRANSFER IBD is on the exact current root-to-Q05931 path. Partner divergence and holdase-versus-foldase limits make this inherited term non-core rather than bad propagation. PomBase:SPAC664.11 SUPPORTS TRANSFER This fission-yeast mitochondrial Hsp70 is a close donor in the current folding-chaperone seed set and supports the broad ancestral node. UniProtKB:P0A6Y8 SUPPORTS TRANSFER Bacterial DnaK is a strong folding-chaperone donor for the broad ancestral term, while Ssq1-specific evidence is narrower. UniProtKB:P0DMV8 SUPPORTS TRANSFER Cytosolic metazoan Hsp70 donors support the ancestral folding placement; this does not by itself make the exact activity core for Ssq1. Supporting Evidence: PMID:11601843 Ssq1 showed typical chaperone properties by binding to unfolded substrate proteins in an ATP-regulated manner. PMID:23615440 purified Ssq1 has been shown to be capable of protecting denatured rhodanese from aggregation in vitro file:yeast/SSQ1/SSQ1-hypotheses/folding-refolding-and-secondary-client-interactions/openscientist.md GO:0044183 protein folding chaperone | MF | IBA (PTHR19375) | Retain as ancestral inference | Legitimate IBA; less precise than direct data |
| GO:0016226 iron-sulfur cluster assembly | IBA GO_REF:0000033 | ACCEPT | Summary: Ssq1 directly contributes to the transfer stage of Fe-S cluster assembly. Reason: Ssq1 is an active chaperone participant: its ATPase cycle controls Isu binding and brings scaffold and Grx5 carrier together for cluster transfer. It need not synthesize the cluster chemically to participate in the assembly pathway. Full PMID:23615440 and PMID:12756240 provide target biochemical evidence for the inferred conserved process. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000452554 SUPPORTS TRANSFER ISC IBD lies on the target lineage and includes target SGD:S000004361. Native transfer mechanism independently supports conservation. SGD:S000004361 SUPPORTS TRANSFER Direct yeast Ssq1 Fe-S evidence is one of the current descendants grounding the conserved mitochondrial ISC node. UniProtKB:P38646 SUPPORTS TRANSFER Human HSPA9/mortalin provides metazoan support for the conserved mitochondrial Hsp70 role in Fe-S biogenesis. CGD:CAL0000196728 SUPPORTS TRANSFER Candida evidence in the current donor set is consistent with retention of the Ssq1-specialized ISC pathway in fungi. Supporting Evidence: PMID:23615440 The vicinity of Isu1 and Grx5 on the Hsp70 chaperone facilitates rapid Fe/S cluster transfer from Isu1 to Grx5. PMID:12756240 Jac1 and Isu1 cooperatively stimulate the ATPase activity of Ssq1. file:yeast/SSQ1/SSQ1-deep-research-falcon.md it promotes **release of a newly assembled Fe–S cluster from the Isu scaffold** |
| GO:0042026 protein refolding | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: General protein refolding overstates the demonstrated Ssq1 holdase and ISC-transfer chemistry. Reason: GO:0042026 requires restoration of biological activity of an unfolded or misfolded protein. The focused report found that the Ssq1 assays demonstrate ATP-regulated unfolded-substrate binding, Nfs1 protection and rhodanese aggregation suppression, but not reactivation of a denatured substrate. The ancestral IBD still lies on the Q05931 path and no NOT/IRD blocks that path, so this is not a stale or formally invalid IBA; it is an over-specific foldase process for Ssq1's better-supported holdase/escort role in Fe-S cluster transfer. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000452648 SUPPORTS SOURCE BUT NOT TARGET The refolding IBD and target ancestry are current, but target assays establish holdase and ISC-transfer activities rather than productive refolding. SGD:S000000004 SUPPORTS SOURCE BUT NOT TARGET Yeast Ssa1 currently seeds refolding at the broad Hsp70 node; that supports the ancestor without proving the specialized Ssq1 substrate outcome. SGD:S000003806 SUPPORTS SOURCE BUT NOT TARGET The general mitochondrial Hsp70 Ssc1 also seeds this broad node, yet its folding role is broader than the specialized Ssq1/Jac1/Isu cycle. UniProtKB:P0DMV8 SUPPORTS SOURCE BUT NOT TARGET Human cytosolic Hsp70 evidence supports the PAINT ancestor while leaving the Ssq1-specific foldase claim over-specific. Supporting Evidence: PMID:23615440 purified Ssq1 has been shown to be capable of protecting denatured rhodanese from aggregation in vitro PMID:11601843 Ssq1 showed typical chaperone properties by binding to unfolded substrate proteins in an ATP-regulated manner. file:yeast/SSQ1/SSQ1-hypotheses/folding-refolding-and-secondary-client-interactions/openscientist.md GO:0042026 protein refolding | BP | IBA (PTHR19375) | Flag non-core / caveat | No Ssq1 reactivation assay; over-reaching file:interpro/panther/PTHR19375/PTHR19375-paint.tsv PTHR19375 PTN001065099 GO:0006457 P IBA false PANTHER:PTN000452648 taxon:4751 20260616 PTHR19375 PTN001065099 GO:0042026 P IRD true PANTHER:PTN000452648 taxon:4751 20260616 |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | Summary: ATP binding is integral to the Ssq1 ATPase cycle. Reason: Full PMID:12756240 isolates Ssq1 bound to radiolabeled ATP, measures its conversion to ADP, and characterizes nucleotide release. A correct binding annotation is core even when a catalytic annotation gives additional information. Supporting Evidence: PMID:12756240 Jac1 and Isu1 cooperatively stimulate the ATPase activity of Ssq1. |
| GO:0005739 mitochondrion | IEA GO_REF:0000117 | ACCEPT | Summary: Mitochondria are the core compartment of Ssq1-mediated Fe-S maturation. Reason: Ssq1 performs its established Fe-S transfer role in the mitochondrial matrix. The organelle parent represents that core location and is not downgraded because a matrix child term also exists. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0005759 mitochondrial matrix | IEA GO_REF:0000044 | ACCEPT | Summary: Ssq1 functions in the mitochondrial matrix. Reason: Target localization and organellar functional studies place Ssq1 in the matrix, where Isu, Jac1 and Grx5 cooperate in Fe-S maturation. PMID:8707841 used the historical SSH1 name for this Hsp70, also tracked in later Ssq1 literature; this should not be confused with the modern ER translocon gene sharing that old name. This location is supported positively and is not an exclusivity claim. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0016887 ATP hydrolysis activity | IEA GO_REF:0000002 | ACCEPT | Summary: ATP hydrolysis powers the specialized Ssq1 chaperone cycle. Reason: Full PMID:12756240 measures single-turnover ATP-to-ADP conversion and steady-state activity of purified Ssq1. Jac1 and Isu1 act cooperatively; Mge1 supports nucleotide release and cycling. These are direct catalytic measurements, independently supporting the family/mapping assertions. Supporting Evidence: PMID:12756240 Jac1 and Isu1 cooperatively stimulate the ATPase activity of Ssq1. |
| GO:0070013 intracellular organelle lumen | IEA GO_REF:0000117 | ACCEPT | Summary: The mitochondrial matrix is an intracellular organelle lumen. Reason: The broad location follows from the experimentally supported matrix pool. Redundancy with a precise term is not evidence of over-annotation or a reason to classify the location as peripheral. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0005515 protein binding | IPI PMID:12756240 Ssq1, a mitochondrial Hsp70 involved in iron-sulfur (Fe/S) c... | REMOVE | Summary: The reported Isu1 interaction is meaningful, but generic protein binding is uninformative. Reason: The full source directly measures Ssq1-Isu1 interaction by SPR and nucleotide-dependent glycerol-gradient association, with Jac1 promoting client engagement. Remove only this nonspecific molecular-function label under the protein-binding review policy, not the interaction evidence. Retain the established client-binding mechanism in the description, core function and references. A folding-specific replacement is not manufactured from binding alone while its functional scope remains under adjudication. Supporting Evidence: PMID:12756240 Isu, the proposed scaffold on which Fe/S centers are assembled, is a substrate for both Jac1 and Ssq1. |
| GO:0005515 protein binding | IPI PMID:12947415 An interaction between frataxin and Isu1/Nfs1 that is crucia... | REMOVE | Summary: The reported Isu1 interaction is meaningful, but generic protein binding is uninformative. Reason: The source reports Isu1-GST copurification and competition with native Isu1 supporting association with Ssq1; the source is about frataxin but also assays this interaction. Remove only this nonspecific molecular-function label under the protein-binding review policy, not the interaction evidence. Retain the established client-binding mechanism in the description, core function and references. A folding-specific replacement is not manufactured from binding alone while its functional scope remains under adjudication. Supporting Evidence: PMID:12756240 Isu, the proposed scaffold on which Fe/S centers are assembled, is a substrate for both Jac1 and Ssq1. |
| GO:0005515 protein binding | IPI PMID:37968396 The social and structural architecture of the yeast protein ... | REMOVE | Summary: The reported Isu1 interaction is meaningful, but generic protein binding is uninformative. Reason: The source uses endogenous GFP pull-down/MS and reports an Isu1 interaction in the curated annotation; the specific supplementary interaction-score entry has not been independently rechecked. Remove only this nonspecific molecular-function label under the protein-binding review policy, not the interaction evidence. Retain the established client-binding mechanism in the description, core function and references. A folding-specific replacement is not manufactured from binding alone while its functional scope remains under adjudication. Supporting Evidence: PMID:12756240 Isu, the proposed scaffold on which Fe/S centers are assembled, is a substrate for both Jac1 and Ssq1. |
| GO:0016226 iron-sulfur cluster assembly | IMP PMID:11171977 Jac1, a mitochondrial J-type chaperone, is involved in the b... | ACCEPT | Summary: Ssq1 loss impairs Fe-S enzyme function independently of excess mitochondrial iron. Reason: The source PMID:11171977 explicitly tests ssq1 as well as jac1 mutants. Fe-S enzyme activities remain low when normal mitochondrial iron levels are maintained, supporting a biogenesis defect beyond secondary iron toxicity. The exact transfer-stage placement comes from additional biochemical studies, not an Isu-accumulation assay claimed for this paper. Supporting Evidence: PMID:11171977 Fe/S enzyme activities remain low in both jac1 and ssq1 mutant mitochondria even if normal mitochondrial iron levels are maintained. PMID:23615440 The vicinity of Isu1 and Grx5 on the Hsp70 chaperone facilitates rapid Fe/S cluster transfer from Isu1 to Grx5. |
| GO:0044571 [2Fe-2S] cluster assembly | IMP PMID:11273703 The mitochondrial proteins Ssq1 and Jac1 are required for th... | ACCEPT | Summary: Ssq1 contributes to maturation of [2Fe-2S] proteins. Reason: The source PMID:11273703 measures conversion of mitochondrial apoferredoxin to Fe-S-containing holoferredoxin and requires Ssq1 and Jac1. The native Isu-to-Grx5 transfer mechanism explains participation without assigning the initial cluster-synthesis chemistry to Ssq1. Supporting Evidence: PMID:11273703 Employing an assay that allowed us to monitor the conversion of the apoform of mitochondrial ferredoxin into its FeS-containing holoform, Ssq1 was demonstrated to be required for the FeS cluster assembly in mitochondria. PMID:23615440 The vicinity of Isu1 and Grx5 on the Hsp70 chaperone facilitates rapid Fe/S cluster transfer from Isu1 to Grx5. |
| GO:0005739 mitochondrion | IMP PMID:11273703 The mitochondrial proteins Ssq1 and Jac1 are required for th... | ACCEPT | Summary: Mitochondria are the core compartment of Ssq1-mediated Fe-S maturation. Reason: Ssq1 performs its established Fe-S transfer role in the mitochondrial matrix. The organelle parent represents that core location and is not downgraded because a matrix child term also exists. PMID:11273703 directly studies Ssq1-dependent holoferredoxin formation in isolated mitochondria. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0006879 intracellular iron ion homeostasis | IMP PMID:9660806 Mt-Hsp70 homolog, Ssc2p, required for maturation of yeast fr... | KEEP AS NON CORE | Summary: Ssq1 dysfunction perturbs cellular iron homeostasis. Reason: The source PMID:9660806 explicitly identifies Ssc2p and reports increased cellular iron uptake and mitochondrial accumulation in mutants. This is a supported consequence of its Fe-S machinery role, retained as physiological context. It does not establish that Ssq1 itself transports iron or donates iron to a scaffold. Supporting Evidence: PMID:9660806 These mutants exhibit increased cellular iron uptake, and the iron accumulates exclusively within mitochondria. |
| GO:0016887 ATP hydrolysis activity | IDA PMID:12756240 Ssq1, a mitochondrial Hsp70 involved in iron-sulfur (Fe/S) c... | ACCEPT | Summary: ATP hydrolysis powers the specialized Ssq1 chaperone cycle. Reason: Full PMID:12756240 measures single-turnover ATP-to-ADP conversion and steady-state activity of purified Ssq1. Jac1 and Isu1 act cooperatively; Mge1 supports nucleotide release and cycling. These are direct catalytic measurements, independently supporting the family/mapping assertions. Supporting Evidence: PMID:12756240 Jac1 and Isu1 cooperatively stimulate the ATPase activity of Ssq1. |
| GO:0005739 mitochondrion | HDA PMID:24769239 Quantitative variations of the mitochondrial proteome and ph... | ACCEPT | Summary: Mitochondria are the core compartment of Ssq1-mediated Fe-S maturation. Reason: Ssq1 performs its established Fe-S transfer role in the mitochondrial matrix. The organelle parent represents that core location and is not downgraded because a matrix child term also exists. The cited mitochondrial proteomics study is available as an abstract; its source-specific peptide entry was not independently rechecked. Retention also rests on independent target localization and organellar biochemistry, not on a claim that this abstract lists Ssq1. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0005739 mitochondrion | HDA PMID:16823961 Toward the complete yeast mitochondrial proteome: multidimen... | ACCEPT | Summary: Mitochondria are the core compartment of Ssq1-mediated Fe-S maturation. Reason: Ssq1 performs its established Fe-S transfer role in the mitochondrial matrix. The organelle parent represents that core location and is not downgraded because a matrix child term also exists. The cited mitochondrial proteomics study is available as an abstract; its source-specific peptide entry was not independently rechecked. Retention also rests on independent target localization and organellar biochemistry, not on a claim that this abstract lists Ssq1. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0005759 mitochondrial matrix | IDA PMID:8707841 The cold sensitivity of a mutant of Saccharomyces cerevisiae... | ACCEPT | Summary: Ssq1 functions in the mitochondrial matrix. Reason: Target localization and organellar functional studies place Ssq1 in the matrix, where Isu, Jac1 and Grx5 cooperate in Fe-S maturation. PMID:8707841 used the historical SSH1 name for this Hsp70, also tracked in later Ssq1 literature; this should not be confused with the modern ER translocon gene sharing that old name. This location is supported positively and is not an exclusivity claim. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0016226 iron-sulfur cluster assembly | IMP PMID:9813017 Suppressors of superoxide dismutase (SOD1) deficiency in Sac... | ACCEPT | Summary: SSQ1 contributes to Fe-S cluster biogenesis. Reason: The source PMID:9813017 directly includes SSQ1 along with JAC1 and NFU1 and reports reduced activities of Fe-S enzymes in relevant null mutants. Later Ssq1 client-binding and transfer studies establish that the protein performs a chaperone step in the process, strengthening the original genetic inference. Supporting Evidence: PMID:23615440 The vicinity of Isu1 and Grx5 on the Hsp70 chaperone facilitates rapid Fe/S cluster transfer from Isu1 to Grx5. |
| GO:0005759 mitochondrial matrix | EXP PMID:10779357 Role of the mitochondrial Hsp70s, Ssc1 and Ssq1, in the matu... | ACCEPT | Summary: Ssq1 localizes to the mitochondrial matrix. Reason: PMID:10779357 explicitly places Ssq1 in the yeast mitochondrial matrix, and the rest of the Ssq1 Fe-S maturation literature supports that compartment as the site of its native Isu/Jac1/Mge1/Grx5 cycle. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0005759 mitochondrial matrix | EXP PMID:11273703 The mitochondrial proteins Ssq1 and Jac1 are required for th... | ACCEPT | Summary: Ssq1 localizes to the mitochondrial matrix where it supports Fe-S cluster assembly. Reason: PMID:11273703 directly assays mitochondrial Fe-S cluster assembly and is consistent with independent Ssq1 matrix localization. This experimental location agrees with the accepted matrix and mitochondrion rows. Supporting Evidence: PMID:10779357 The mitochondrial matrix of the yeast Saccharomyces cerevisiae contains two molecular chaperones of the Hsp70 class, Ssc1 and Ssq1. |
| GO:0016887 ATP hydrolysis activity | EXP PMID:16431909 The Hsp70 chaperone Ssq1p is dispensable for iron-sulfur clu... | ACCEPT | Summary: Ssq1 ATPase activity is supported by biochemical work on the purified ISC chaperone system. Reason: PMID:16431909 studies the specialized yeast mitochondrial Ssq1/Jac1/Mge1 system with purified proteins and complements direct PMID:12756240 ATPase measurements. The ATPase term is central to Ssq1's Hsp70 chaperone cycle. Supporting Evidence: PMID:12756240 Jac1 and Isu1 cooperatively stimulate the ATPase activity of Ssq1. |
| GO:0016887 ATP hydrolysis activity | EXP PMID:26545917 Iron-Sulfur Cluster Biogenesis Chaperones: Evidence for Emer... | ACCEPT | Summary: Ssq1 ATPase activity is part of a conserved Jac1-coupled ISC chaperone cycle. Reason: PMID:26545917 tests Ssq1/Jac1 partner specificity and HPD-mutant stimulation in the specialized Fe-S biogenesis chaperone system. It corroborates Ssq1 as an Hsp70-family ATPase without changing the core direct evidence from PMID:12756240. Supporting Evidence: PMID:12756240 Jac1 and Isu1 cooperatively stimulate the ATPase activity of Ssq1. |
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Download this section (compressed HTML)Q: Which Ssq1 assays demonstrate restoration of a client protein folding state or activity, and which establish only antiaggregation or ATP-driven Isu remodeling? Can GO:0044183, GO:0042026, GO:0140662 or GO:0140309 be distinguished without treating native client specialization as a universal functional loss?
Q: Does the Nop1-bait/Ssq1 association in PMID:19536198 TableS2 persist in intact cells or compartment-preserving assays, and is it independent of the earlier PMID:16554755 dataset? Which physiological interaction, if any, explains it without inferring nuclear Ssq1 residence from lysate copurification?
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Download this section (compressed HTML)Mitochondrial hsp70-type molecular chaperone; required for assembly of iron/sulfur clusters into proteins at a step after cluster synthesis; involved in maturation of Grx5p and Yfh1p, which is a homolog of human frataxin implicated in Friedreich's ataxia
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